The overall objective of the proposed research is to further develop and test an NaOH in FC-80 fluorocarbon emulsion to enable liquid-breathing normothermic mammals to maintain respiratory homeostasis. It is believed that hypercapnia and oxygen toxicity can be avoided by using a liquid that combines the high oxygen solubility of FC-80 fluorocarbon with the chemical bonding of carbon dioxide by an NaOH solution. Anesthetized normothermic beagle dogs will be ventilated mechanically with either FC-80 fluorocarbon or an NaOH in FC-80 fluorocarbon emulsion to compare the relative efficiencies of these two liquids in CO2 removal at different levels of alveolar ventilation. Volume-flow characteristics of emulsion-filled excised dogs' lungs will be determined by volume displacement plethysmography. Microscopic examinations of lungs from both dogs and mice will be conducted at various times (1 day to 2 years) subsequent to emulsion breathing for evidence of toxic effects. The development of a suitable breathing liquid is a prerequisite to differentiate between the pharmacological effects of gases and the effects of hydrostatic pressure per se in biological processes in mammals.